Thanks, Paul.
If I understand correctly, "degree of curvature" is how tight a curve is. Is there a term for simply how much (in degrees) a single curve changes the direction of the rail line (regardless of the radius)?
Which begs the question: are any curves in railroading either increasing-radius or decreasing-radius ones. (Both of those commonly exist on roads and auto racing tracks.) Or are they all constant-radius curves? Most would be connected by tangents; but, say, a crossover would be two curves end to end, one a left and the other a right, or vice versa.
Lithonia Operator Which begs the question: are any curves in railroading either increasing-radius or decreasing-radius ones. (Both of those commonly exist on roads and auto racing tracks.) Or are they all constant-radius curves?
Which begs the question: are any curves in railroading either increasing-radius or decreasing-radius ones. (Both of those commonly exist on roads and auto racing tracks.) Or are they all constant-radius curves?
Most/all mainline curves include increasing-radius and decreasing radius curves. They are called "easements".
Most would be connected by tangents; but, say, a crossover would be two curves end to end, one a left and the other a right, or vice versa.
A crossover track is NOT two curves end to end. The curves are all incorporated in the closure rails, which run between the points and the frog. Between the two frogs, all the track is normally straight.
Ed
7j43k Lithonia Operator Which begs the question: are any curves in railroading either increasing-radius or decreasing-radius ones. (Both of those commonly exist on roads and auto racing tracks.) Or are they all constant-radius curves? Most/all mainline curves include increasing-radius and decreasing radius curves. They are called "easements". Most would be connected by tangents; but, say, a crossover would be two curves end to end, one a left and the other a right, or vice versa. A crossover track is NOT two curves end to end. The curves are all incorporated in the closure rails, which run between the points and the frog. Between the two frogs, all the track is normally straight. Ed
Thanks, Ed. I've learned a lot today.
Lithonia OperatorThanks, Paul. If I understand correctly, "degree of curvature" is how tight a curve is. Is there a term for simply how much (in degrees) a single curve changes the direction of the rail line (regardless of the radius)? Which begs the question: are any curves in railroading either increasing-radius or decreasing-radius ones. (Both of those commonly exist on roads and auto racing tracks.) Or are they all constant-radius curves? Most would be connected by tangents; but, say, a crossover would be two curves end to end, one a left and the other a right, or vice versa.
Regardless of increasing or decreasing radius of the curves - the speed restriction for that segment of track will be set by the requirements of the sharpest of the curves.
As a race driver you want to maximize your speed to the limit of each segment of a curve - no matter if that particular segment is increasing or decreasing in its radius. On the railroad one speed fits all and that limit applies to the entire length of the train.
Never too old to have a happy childhood!
Low speed curves with little or no superelevation are often nominally a constant-radius curve, although as a practical matter the stiffness of the rails imparts a little spiral at the ends.
Spiral is the universal term for the increasing radius and decreasing radius curves, which are used mainly for higher speed tracks, those with sharper curves, or where a lot of superelevation is needed. Usually the radius at the beginning of the curve is infinite = tangent, then it gets progressively sharper until it matches the constant-radius part. Aside from easing into the curve, one important reason is to be able to gradually increase the supelevation from 0" on the tangent to the proper value in the body of the curve. The details of all this are beyond the scope of this forum, and take up chapters in books on route or track alignment/ surveying and professional papers. Despite this being a relatively settled field, some of these are surprisingly recent - e.g., A Better Way to Design Railroad Transition Spirals by Louis T. Klauder Jr., PhD, PE., (c) 2001 by Louis T. Klauder, Jr., can be found at https://www.arema.org/files/comm/c17/Milwaukee_22.PDF )
For most crossovers the short segment of track between the frogs of the respective turnouts are tangent. However, there are some situations where the turnout/ frog numbers are not identical - say, a No. 12 in one track, and a No. 10 in the other - where a small curve must be introduced so the alignment is continuous and smooth; that can also happen where the tracks have an angle spreading apart, and other unusual configurations.
- PDN.
I tried to determine the radius of the curve from a large-scale (1" = 20') print of it from Google Maps Satellite View. However, there's the apparent kink I noted previously just before leaving the bridge in a SW directon, and then a flat spot just after arriving on 'dry land' opposite the angle in the adjacent Appalachian Trail walkway (which is to the SE). Those are likely distortions from Google Maps, not real-life track configurations. As a result, I would not put much faith in any curve radius determination based on the Google Maps Satellite View.
That said - and having read a little about the history of track relocations in this area over the years - as I said before, it could be 12 to 15 degrees, and I'm now leaning more towards the 15 - 16 degree range. Although it may be termed a "main track", it's more like a secondary/ branch line. Such curves - while certainly not desirable - may be a result of history and a present-day fact of life for the railroads that have inherited them and must still operate over them today.
References on the history of the Harpers Ferry bridges:
http://www.wvculture.org/shpo/nr/pdf/jefferson/78001484.pdf - Nomination Form for National Register of Historic Places Inventory, a really detailed explanation.
The short version - https://en.wikipedia.org/wiki/B_%26_O_Railroad_Potomac_River_Crossing
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